This application incorporates by reference Taiwan application Serial No. 090212848, filed Jul. 27, 2001.
1. Field of the Invention
This invention relates in general to a controlling apparatus. More specifically, the invention relates to an apparatus for controlling a rotational speed of a motor.
2. Description of Related Art
With the high technological progress and development in the computer industry, precise electronic products, such as the notebook computer, the scanner and the power supply, are widely used. In order to satisfy users"" requirements for convenience and efficiency, it becomes a key issue for all makers to make products that have reduced volume becomes and higher operational speed. The key point as to whether the compact electronic products can have maximum efficiency depends on whether the heat generated by the electronic devices in the product can be quickly dissipated. When the heat cannot be efficiently dissipated in time and sinks into the products, the temperature inside the products will increase, causing that the electronic devices in the products not to function normally. As a result, the efficiency of the product is affected, or even the product may malfunction or break down. In order to dissipate the heat quickly, the maker usually assembles a fan in its products to serve as a heat dissipation device, so that the electronic products can work in a proper environment. Because the fan is driven by a DC motor, the rotational condition of the motor will affect the rotational speed of the fan, and therefore affect the heat dissipation effect.
FIG. 1 shows a block diagram of a conventional controlling apparatus for a brushless DC motor. The conventional controlling apparatus for the motor is composed of a controlling unit 102 and a driving unit 104. The controlling unit 102 outputs a controlling signal to the driving unit 104, in which the controlling signal is a DC voltage signal. In a DC motor controlling apparatus capable of controlling its fan speed, the controlling unit 102 is in fact a linear regulator that receives a fixed DC voltage signal and then outputs the controlling signal. The voltage value depends on the temperature at which the electronic device operates currently. The driving unit 104 is a power amplifier equivalently, and can output a DC voltage driving signal with a fixed value, thereby to control the motor rotor to rotate at a fixed rotational speed. It should be noted that the rotational speed of the motor is controlled by the voltage value of the controlling signal output from the controlling unit 102. Therefore, by controlling the voltage value of the controlling signal output from the controlling unit 102, the rotational speed of the fan can be controlled so as to have the best heat dissipation.
The conventional controlling apparatus for the motor has the following shortcomings. First, some problems occur easily in manufacturing the conventional controlling apparatus, for example, deviations of mechanism assemble, shape variations of the coil, washer deformation, or bad lubrication of bearings, etc. Therefore, different motors have deviations in structure. When the driving unit drives the motor according to the same DC voltage controlling signal output from the controlling unit, different motors will have different rotational speeds. Accordingly, the corresponding relationships between the rotational speed of the motor and the DC voltage controlling signal from the driving unit are different among different motors. As a result, the products have to be tested, adjusted or selected eliminate products that do not meet the preset specifications, causing waste in manufacturing cost and time.
In addition, as described above, the value of the voltage signal from the controlling unit depends on the rotational speed of the motor. When the motor operates at full speed, the voltage value of the controlling signal output from the controlling unit is equal to the received voltage signal. However, when the motor does not need to operate at full speed, the voltage value of the controlling signal output from the controlling unit is less than the received voltage signal. At this time, additional energy will be consumed in the form of heat, so as to reduce the dissipation effect of the heat dissipation device.
To overcome problems presented the foregoing description, an object of this invention is to provide an apparatus for controlling the rotational speed of the motor, by which wastes of time and cost in selecting products can be reduced, and the energy waste when the motor does not operate at full speed can be reduced.
To achieve the above objects, the invention provides an apparatus for controlling the rotational speed of a motor to control the rotational speed of a motor rotor, and additionally, the apparatus is coupled to a sensing unit. The apparatus comprises a controlling unit, coupled to the sensing unit, for outputting a controlling signal according to the sensing signal, wherein the controlling signal is a square wave and has a duty ratio that is determined by the sensing signal; and a driving unit, coupled to the controlling unit, for outputting a driving signal to a motor rotor according to the duty ratio of the controlling signal, wherein the driving signal is a square wave, and the rotational speed of the motor rotor is determined by the duty ratio of the driving signal.